1. Field of the Invention
This invention relates to devices for measuring nerve conduction in peripheral nerves and more particularly, to such devices that measure the conduction time and amplitude of a test signal applied to a peripheral nerve.
2. Description of the Related Art
It is common practice in medicine to measure the electrical conduction on a peripheral nerve. A common use of this test is diagnosing carpel tunnel syndrome when electrical conduction in the median nerve is measured across the wrist. During the test, the physician measures the conduction time and the amplitude (compound muscle action potential or sensory nerve action potential) of the nerve by stimulating the nerve with a nerve stimulator. When setting up for the test, the active recording electrode and a second electrode, called reference recording electrode is attached to the patient's skin over the nerve or the muscle activated nerve. A ground-recording electrode is attached nearby to the skin. The nerve stimulator is then applied to the skin at a pre-measured distance from the active recording electrode.
When testing for carpel tunnel syndrome, the active and reference recording electrodes and the nerve stimulator's cathode probe are spaced apart over the hand and forearm at several known distances (8 cm, 10 cm, and 14 cm). Heretofore, physicians have used a ruler and an ink marker to first mark the specific locations on the forearm where the active recording electrode and the stimulator's cathode probe should be placed during the test. Often, several tests are performed that requires manually marking several sets of reference points on the skin. The act of measuring and marking several sets of reference points on the forearm and hand is very time consuming. Also, because the sets of marked points are relatively close, a wrong set of reference points may be used during the test that produces inaccurate readings.